Seasonality and interannual variability of CH(4) fluxes from the eastern Amazon Basin inferred from atmospheric mole fraction profiles

The Amazon Basin is an important region for global CH(4) emissions. It hosts the largest area of humid tropical forests, and around 20% of this area is seasonally flooded. In a warming climate it is possible that CH(4) emissions from the Amazon will increase both as a result of increased temperatures and precipitation. To examine if there are indications of first signs of such changes we present here a 13 year (2000–2013) record of regularly measured vertical CH(4) mole fraction profiles above the eastern Brazilian Amazon, sensitive to fluxes from the region upwind of Santarém (SAN), between SAN and the Atlantic coast. Using a simple mass balance approach, we find substantial CH(4) emissions with an annual average flux of 52.8 ± 6.8 mg CH(4) m(−2) d(−1) over an area of approximately 1 × 10(6) km(2). Fluxes are highest in two periods of the year: in the beginning of the wet season and during the dry season. Using a CO:CH(4) emission factor estimated from the profile data, we estimated a contribution of biomass burning of around 15% to the total flux in the dry season, indicating that biogenic emissions dominate the CH(4) flux. This 13 year record shows that CH(4) emissions upwind of SAN varied over the years, with highest emissions in 2008 (around 25% higher than in 2007), mainly during the wet season, representing 19% of the observed global increase in this year.